Bilbao, Spain - Suspected members of the militant Basque separatist group ETA planted a bomb in the Basque city of Bilbao early Thursday, causing slight injuries to three police officers, officials said.

The bomb, which exploded at an office of the Basque branch of Spanish Prime Minister Jose Luis Rodriguez Zapatero's Socialist Party, caused material damage. The police officers suffered ear pain.

Patrolling police officers spotted the bomb at 5 am (3 am GMT) and evacuated the area. A caller speaking in the name of ETA then warned a rescue service that a bomb was about to go off. (dpa)